In a manufacturing process of a semiconductor device, various processes such as an etching process, an ashing process and a film forming process have been performed on a semiconductor wafer as a target object. In these processes, there has been used a plasma processing apparatus configured to perform a plasma process on the semiconductor wafer in a processing chamber capable of maintaining a vacuum atmosphere.
Recently, a semiconductor wafer has become larger and a device has become miniaturized. In response to this trend, it has been required to enhance efficiency (for example, a film forming rate) in a plasma process and uniformity of a process on a wafer surface. For this reason, attention is drawn to a method for performing a plasma process while a bias voltage is applied to a semiconductor wafer and a high frequency power is applied to an electrode embedded in a mounting table for mounting thereon a semiconductor wafer within a processing chamber of a plasma processing apparatus (for example, Patent Document 1).
If the high frequency power is applied to the electrode embedded in the mounting table, a conductive member, having a ground potential, positioned over a plasma generation space with respect to the electrode embedded in the mounting table may serve as a facing electrode. That is, if the high frequency bias power is applied to the electrode within the mounting table, there is formed a path of a high frequency current (a RF return circuit) from this mounting table to the facing electrode via plasma and from the facing electrode to an earth of a high frequency bias power supply via a wall of the processing chamber. If the path of the high frequency current is not formed stably, an oscillation amplitude of a plasma potential (Vp) generated within the processing chamber becomes large, and, thus, the plasma process cannot be performed stably. Further, if the oscillation amplitude of the plasma potential is large, particularly when a process is performed at a low pressure of several tens Pa or less, a surface of the facing electrode typically made of aluminum may be sputtered by the plasma, resulting in contamination. In order to suppress oscillation of the plasma potential, the facing electrode needs to have a sufficiently large area. However, in a conventional microwave plasma processing apparatus described in Patent Document 1, a microwave transmissive plate is provided at an upper region of the processing chamber. Thus, unlike a parallel plate type plasma processing apparatus, it is difficult for the facing electrode to have a sufficiently large area due to a design limitation of the apparatus.
In this regard, as a microwave plasma processing apparatus, there has been suggested a plasma processing apparatus capable of detachably attaching an annular facing electrode made of silicon or aluminum to a periphery of a microwave transmissive plate within a processing chamber (for example, Patent Documents 2 and 3). In a conventional technique described in Patent Documents 2 and 3, the facing electrode has a sufficiently large area. Thus, when a high frequency power is applied to a mounting table, a plasma potential (Vp) can be stabilized. However, since the facing electrode described in Patent Documents 2 and 3 is provided so as to closely come into contact with the microwave transmissive plate, an effective area for introducing a microwave becomes smaller and the microwave is introduced unstably. Thus, plasma may be generated unstably in the processing chamber. Further, in the microwave plasma processing apparatus, plasma is generated right below the microwave transmissive plate, and, thus, a temperature of electrons is the highest in the vicinity of the microwave transmissive plate. For this reason, if the facing electrode closely comes into contact with the microwave transmissive plate so as to protrude toward a processing space as described in Patent Documents 2 and 3, a front end of the facing electrode can be sputtered by the plasma easily and contamination may occur.    Patent Document 1: PCT Publication No. WO2009/123198 A1    Patent Document 2: Japanese Patent Laid-open Publication No. H09-266095    Patent Document 3: Japanese Patent Laid-open Publication No. H10-214823